Method for heat treating hot rolled steel rods



Dec. 5, 1961 METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan.18, 1960 WATER DRA'N SUPPLY ATOMIZER '3 Sheets-Sheet 1 FlG.l

Dec. 5, 1961 J B. KOPEC ETAL 3,011,928

METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan. 18, 1960 '3Sheets-Sheet 2 Dec. 5, 1961 J B. KOPEC ETAL 3,011,928

METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan. 18, 1960 v 3Sheets-Sheet 3 United States Patent 3,011,928 METHOD FOR HEAT TREATINGHOT ROLLED STEEL RODS 3 Benedict Kopec, Hamilton Square, and William A.Miller, Roebling, N.J., assignors, by mesne msignments, to MorganConstruction Company, Worcester, Mass a corporation of Massachuse.

Filed Jan. 18, 1960, Ser. No. 3,185 12 Claims. (Cl. 148-156) The presentinvention relates to heat treating carbon steel rods and moreparticularly to a method for heat treating hot rolled carbon steel rodsto render them suitable for being drawn into wire.

In producing high tensile steel wire it has been for many years commonpractice to process high carbon hot rolled steel rod by cold drawingthrough a series of successively smaller dies. With each successive colddrawing the wire becomes harder and more brittle. Consequently, there isa limit to the total percentage in cross-sectional area reduction whichcan be achieved before the wire becomes so hard and brittle that furtherdrawing will cause splitting, breaking or other damage to the wire. Whenthis point is reached the wire may be subjected to a heat treatingprocess, commonly termed patenting after which further wire drawing canbe accomplished, followed in many cases by an additional patenting stepand further cold drawing.

The amount of area reduction which can be achieved before it isnecessary to subject the wire to a patenting operation and the number ofpatenting operations required are of substantial economic importancebecause of the cost involved in performing a patenting operation. Thepercentage area reduction of a hot rolled rod which can be achievedbefore a patenting operation is needed depends upon two principalfactors, namely, the carbon content of the steel and the distribution ofthe carbon in the steel. An important aspect of the invention isconcerned with high carbon steel (that containing 0.4% or more ofcarbon) and a principal object of the invention is to provide a noveland improved method for altering the distribution of the carbon in highcarbon hot rolled rod to facilitate subsequent wire drawin operations.

As steel rod leaves the finishing stand of a continuous hot rollingmill, its temperature will generally be in the range of about 1650-1800F. With temperatures of this order, the carbon will be in solid solutionin the iron. When hot rolled rod cools to a temperature below a criticaltemperature of about 1340 F, the carbon comes out of solution in theform of colonies of parallel plates of iron carbide (cemeutite) in amatrix of iron. This structure is commonly called pearlite. The actualtemperature at which the carbon comes out of solution has importantmetallurgical significance. Thus, at temperatures in the area of thecritical temperature the carbides separate as thick plates, commonlytermed coarse pearlite. These thick plates of iron carbide are brittleand tend to fracture during wire drawing. At a temperature of about 1225F. the plates of iron carbide formed as the carbon comes out of solutionare much thinner, and the rod is much more suitable for drawingpurposes. At a temperature of about l025 F. the plates of iron carbideare Xtremely fine, being visible only under the resolving power of anelectron microscope. The amount of cold wire drawing which can beaccomplished without damage to the wire depends primarily on thefineness of the pearlite structure, and this in turn depends upon thetemperature at which the carbon comes out or" solution.

At temperatures between about 925-425f F. the carbides come out ofsolution in a different form. They have an acicular structure commonlytermed bainite. At temperatures below about 425 F. the steel transformsto 2 martensite. Bainite has inferior ductility, while marteusite isvery hard and brittle.

The rate at which the carbon comes out of solution also varies widelywith temperature, being relatively low at the critical temperature andbeing a maximum at about 1025 F. Below 1025 F. the rate decreases. inthe tem *erature range of about 900l300 F. the carbides will come out ofsolution to form pearlite plates of sufiicient fineness for satisfactorydrawing. Of course, it is important that both the center and the outsideof the rod be maintained within the suitable temperature range while thecarbon comes out of solution to prevent the formation of substantialcoarse pearlite structure at the center or bainitic or martensitestructure at the 811118.86, a problem complicated by the high hotrolling finishing speed usually used, i.e., about 3000-5000 feet perminute. By suitable temperature range is meant that range in which theseparated carbide is in the form of fine pearlite suitable for wiredrawing without further heat treatment, namely, about 900-1300" F, andpreferably about 1000-1225 F.

The metallurgical principles discussed above have been understood bythose skilled in the art and various efforts have been made to provideproper heat treatment of the rod as it leaves the hot rolling mill. Aparticularly satisfactory method of effecting such heat treating tosecure a fine pearlitic structure suitable for wire drawing is describedin United States Patent 2,75 6,169 to Cots-on, Goetz and Lewis.

Other examples of efiorts to cool high carbon hot rolled rod as itemerges from the rod mill are described in United States Patents2,621,914 to Morgan, 2,810,569 to Morgan and Wilson, 2,810,570 toWilson, and 2,819,058 to Morgan, and British Patent 342,189.

The foregoing description has dealt with the advantages of a method forheat treating high carbon steel rod. The method is also advantageous forheat treating low carbon steel rod, i.e., rod having a carbon contentless than about 0.4%. The metallurgical processes involved are the same,but, because of the lower carbon content of the material, themiorostructure consists primarily of grains of iron, commonly calledferrite with comparatively few colonies of pearlite. The effect of theheat treatment of the invention on low carbon steel rod is to obtainuniform small grains of ferrite containing umformly distributed smallcolonies of pearlite.

it is not usual to paten low carbon steel since its inherent ductilityis sufficient for the wire drawing process. Thus, while use of the heattreating process of the invention on low carbon steel will not generallyresult in saving of patenting heat treatments, a considerable advantagewill nevertheless be achieved because of the greater uniformity of coldworking properties in the material. This is particularly advantageouswhen the wire is subject to the variety of cold forming operations incommercial use for shaping low carbon steel.

The principal object of the present invention has been to provide anovel and improved method for cooling hot rolled rod to render the sameconditioned for subsequent cold drawing operations.

More particularly, it has been a principal object of the invention toprovide a novel and improved method for rapidly cooling high speed hotrolled high carbon steel rod so that both the interior and surface ofthe rod rapidly assume temperatures in the range of about 900- 1300 F.,which temperatures are maintained for a sufficient time to permit theseparation of the carbide in the form of fine pearlite suitable for wiredrawing directly without further heat treatment.

Another principal object of the invention has been to provide a noveland improved method for rapidly cooling high speed low carbon steel rodto obtain uniform small colonies of pearlite.

.FIG. 1.

grains of ferrite containing uniformly distributed small Another objectof the invention has been to provide a method of the above type whichinvolves two cooling steps, in a first one of which the rod leaving therolling mill is rapidly cooled to an average temperature not below thecritical temperature and preferably within the range of about 1350-l450F. and a surface temperature not below about 900 F, and in the secondone of which the rod temperature, both interior and surface, is reducedso as to be within the range of about 900-1300" F. and preferably about1000-1225" F.

A feature of the invention has been the provision of a novel andimproved method of the above type in which the reel can be located aconventional relatively short distance from the finishing stand of therolling mill.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

In accordance with the invention, hot rolled carbon steel rod leaving arolling mill is first subjected to a water cooling step in which the rodis cooled as much as possible without producing different microstmcturesat the outside and center. Thus the rod is cooled to an averagetemperature above the critical temperature at which carbide comes out ofSolution and a surface temperature not below about 900 F. By averagetemperature is meant the temperature to which the rod would equalize ifno heat were added or taken away. The rod is then delivered to a reelingmechanism, the rod entering the reel having a surface temperature lyingwithin the range of about 1350-1450" F. The rod is subjected to atomizedwater spray while being taken up on the reel so that the rod temperature(at both center and surface) is reduced during reeling so as to bewithin the range of about 900- 1300 F. and preferably 1000-1225 F.Preferably, the average temperature of the rod at any and all pointsalong the length of the rod is rapidly reduced to the l000l225 F. range.By rapidly is meant about one minute or less.

The invention will now be described in greater detail with reference tothe appended drawings, in which:

FIG. 1 is a diagrammatic illustration of one embodiment of the inventionas'applied to a pouring reel;

FIG. 2 is a partly'diagrammatic illustration'of another embodiment ofthe invention as applied to a laying reel; and

FIG. 3 is a side elevational view, partly in cross section, illustratingone form of apparatus for carrying out a portion of the method of theinvention.

Referring now to the drawings, and more particularly to FIG. 1, thedotted line 10 refers to a length of hot rolled rod which progresses athigh speed from right to left in FIG. 1. The rod is shown asemergingfrom a continuous hot rolling mill, the last or finishing standof which is illustrated at 11. The speed of the rod 10' as it 7 leavesthe finishing stand 11 wouldtypically be of the order of 3000 to 5000feet per minute, but higher or lower rod speeds are sometimes used.

The rod 10 leaving the finishing stand 11 is to be taken pouring reel ora laying reel. A pouring reel is shown in In such a construction thereel is rotated at a speed synchronized with the rod speed and therod ispoured into the annular space between twoconcentric rows of guide pins.The guide pins are indicated at 13 and the reel drive at .14. In alaying reel (asillustrated in FIG. 2) the coil does not rotate and therod is laid onto a stationary plate by a synchronized rotating guide. In'accordance with the invention, the rod is cooled. in

7 two steps. The first cooling occurs between the exit end 7 of the hotrolling mill and the reel, and is arranged to cool I the rod from itstemperature at the exit end of the hot rolling mill (usually aboutl650-l800 F.) to a surface temperature, as it enters the reel, of about1350-1450 F;

This first cooling step, which may be effected in any convenient way,should be conducted so'that the average The rod, as it leaves finishingstand 11, passes through bell-mouthed guide pipe 15, and then through asimilar bell-mouthed guide pipe 16 into a'water cooling chamber 17,which might be of the type shown in United States Patent 2,65 8,012 toStrachan. However, unlike the operation described in the Strachanpatent, the leading end of the rod is cooled to the same extent as theremainder of the rod. Should it be desired not to cool the leading. endof the rod, this leading end would subsequently be cut off anddiscarded. The rod passes through a series of guides 18 Within thechamber 17, Water flowing onto the rod within the guides 18 frornaheader :19 to which water is supplied by a pipe 20. Water is drainedfrom the chamber 17 through a pipe 21.

At the exit end of the chamber 17 the rod 10 enters a pipe 22- whichdirects the rod into the pouring reel 12 in the usual manner. As the rod10 enters the pipe 22 the rod surface may have been cooled to arelatively low temperature, approaching 900 F. The rod surfacetemperature can be controlled by regulating the rate of flow of coolingwater.

Because of the high speed of the rod 10, the center thereof will havecooled substantially less than the surface, so that by appropriateadjustment of the cooling water flow the rod average temperature can bemaintained well above the critical temperature. As the rod 10 passes.through the pipe 22, heat transfer between the interior and exteriorportions of the rod tends to equalize the tent peratures at the surfaceand center of the rod so that as the rod leaves the exit end of pipe 22and passes on to reel 12, the surface temperature will have risen to avalue within the range of about 1350-1450" F., i.e., from a valueslightly above the critical temperature to 1450" F. The center of therod may be at about the same temperature or slightly higher, dependingon the length of the pipe 22. The longer the pipe 22 the more nearlyuniform will be the temperatures across the rod cross section.v

Another desirable form of apparatus to efiect the firstv cooling step ofthe invention is that shown in the afore-- mentioned British Patent342,189 of 1931. Simpler forms of water cooling baths could be usedprovided the specified temperature ranges-are achieved.

In accordance with the invention, a second cooling step occurs while therod is being taken up on the reel. This second cooling step is effectedby directing an atomized water spray on the coil of rod as it is beingformed. Thus the atomized water is directed so as to strike primarilythe uppermost layer of rod on the reel. The waterand air flow rates areadjusted so that all portions of therod (from the surface to the center)are cooled below the critical temperature and within the range of about,900-1300" F. and preferably about l000-1225 F. However, the temperatureof the surface of the rod is not allowed to fall below about 900 F.while the rod is.

P upon a reel 12, which may beof any desired type, e.g., a

The reeling usually requires a time of about one minute for the lengthsofrod normally used so that adequate cooling time at a suitable coolingtemperature is afforded for the carbon to come out of solution and forma finepearlitic structure suitable for wire drawing.

. As shown in FIG. 1, water from a pipe 23 and air from a pipe 24 aremixed in an atomizer 25 and the resultant atomized water is sprayed ontothe rod entering the annular coil-forming space of the reel 12 by meansof a delivery pipe 25. Valves 26' and .27 are provided in the pipes 23and 24, respectively, to permit control of the flow rates of water andair, respectively. The delivery pipe 25' may be disposed so as to directthe atomized spray onto a limited area of the coil as the coil revolvesbeneath the end of the delivery pipe" The actual cooling action is acombination of the cooling effects of heating and evaporating the waterin the spray, contact with the air contained in the spray and cont-actwith air due to the rotation of the coil. Most of the cooling actionwith respect to any short length of rod occurs while that short lengthis near the top of the coil so that substantially un form cooling of allparts of the rod takes place. While a coil is being poured it can beobserved that the rod at the top of the coil is red hot and that thebrightness of the color gradually diminishes to a dark red or blacktoward the bottom of the coil.

It is somewhat more diificult properly to cool the rod when using alaying reel instead of a pouring reel since an atomized spray from asingle stationary nozzle will generally not adequately cool the entirecoil in a laying reel.

In FIG. 2 there is illustrated a laying reel 28 to which is deliveredrod which has been subjected to a first cooling step as described inconnection with FIG. 1. The rod leaves pipe 22 and passes through aspout 29 which is rotated by gears 39 and 31 (suitably powered) so as tolay the rod on a plate 32 in the space between annular rows of pins 33and 34. When a complete coil has been laid, the rows of pins 33 and 34may be retracted, as shown in dotted lines at 33 and 34', so that thecoil can be removed by an intermittently operated conveyor 35.

As the coil is laid by the rotating spout 29, the coil is cooled byatomized Water directed primarily onto the uppermost layer of the coilby a series of circumferentially spaced atomizing nozzles, each of whichmay be of the same type as is shown in FIG. 1. A suflicient number ofsuch spray nozzles should be provided so that the sprays overlap,thereby cooling all portions of the coil. The spray should be adjustedto provide temperature distributions as described in connection withPEG. 1. In general, more total water will be required to cool a coil ona laying reel than on a pouring reel because of the more compact natureof the coil on a laying reel. However, with multiple nozzles, asdescribed, less water per nozzle will be required.

Instead of using multiple nozzles, a laying reel may be cooled by anozzle carried on the laying spout 29. In this case the rotation of thenozzle with the spout will serve to cool all portions of the coil.Moreover, the centrifugal force due to the rotation will assist inatomizing the water, the atomizing action occurring from centrifugalforce being dependent on the speed of rotation. if sumcient atomizingaction occurs, a separate air supply may be dispensed with.

FIG. 3 illustrates a particularly desirable form of apparatus forspraying atom zed water on the coil and may be used with any dmired typeof coiling device, e.g., a pouring reel, as in FIG. 1 or a laying reel,as in FIG. 2. The apparatus comprises an air supply pipe 36, a main aircontrol valve 37, an air flow indicator 38, a quick shut oil vmve 39, awater supply pipe 40, a main water control valve 41, a water flowindicator 42, a quick shut ofi valve 43, a Y fitting 44 and a deliverypipe 45.

The valves 37 and 41 serve to permit adjustment of the air and waterflows, respectively, and the flow indicators, which may be of anyconvenient type, facilitate such adjustment by enabling the flows of airand water to be set readily to values previously found desirable. Thequick shut off valves enable the flows of air and water to be shut ofiwithout disturbing their previous settings. Thus after a complete rodhas been wound on a reel and after adequate cooling of the lastdelivered portion of the rod has occurred, the air and water may be shutofif by closing the valves 39 and 43. When a new rod is to be reeled,the air and water may be turned on again at their former flow ratessimply by fully opening the Valves 39 and 43. Prompt resumption ofproper air and Water flows without delay is of course important,especially in view of the high speed at which the rod is delivered tothe reel.

The water entering the Y fitting 44 is atomized by the entering thisfitting, the resultant atomized water he ing sprayed on the coil throughthe delivery pipe 45, the delivery end of the pipe 45 being disposed sothat the spray will contact the desired coil area.

The spray of atomized Water onto the reel is continued after a rod iscompletely wound for a time sufficient adequately to cool the lastportions of the rod, i.e., the portions forming the uppermost layers onthe completed reel. This time may be made equal to the reel braking andremoval times.

An atomizing nozzle of the type shown in FIG. 3 was used on a pouringreel for a rod finishing 0.218 diameter high carbon steel rod. The rodleaving the finishing stand of the rod mill traveled at about 3500 feetper minute. The rod was subjected to a first cooling step, as describedpreviously, and was then delivered to the pouring reel. It was foundthat satisfactory cooling, i.e., cooling within the temperature rangedescribed pr viously, was achieved with air at between 15 and 30 poundsgauge pressure and an air flow between and 250 cubic feet per minute(measured at atmospheric pressure) and a water flow between 0.25 and 2gallons per minute. It was found preferable to provide air flow between75 and cubic feet per minute and water flow between 0.5 and 1.5 gallonsper minute. The supply pipes 36 and 4-0 were and /4" I.D., respectively,the delivery pipe 45 was /2 1.1). by 24" long, and the legs of the Yfitting 44 were 1" 1.1).

Other atomizing arrangements can, of course, be used in practicing theinvention. For example, atomizing arrangements of the type where airflow inspirates the water by creating a suction or where water isaerated to form air bubbles. Water may be atomized Without using aseparate source of air by supplying water under suitable pressure to anatomizing nozzle of appropriate design. In each of these cases theobject is to supply atomized water to the coil to cool the rod as it isbeing coiled to within the temperature range of about 900 to 1300 F. andpreferably about 1000-1225 F., the surface of the rod not being allowedto drop below about 900 F. during at least most of the coilingoperation. 7

In one example of the invention, some 0.187" diameter steel rodcontaining 0.65% carbon left the rolling mill at a temperature between1700 and 1800 F.,-was subjected to the first cooling step of theinvention and was then delivered to a pouring reel. The surfacetemperature of the red as it entered the pouring reel was 1400 F. Therod was sprayed with atomized water as it was reeled, the flow ofatomized water being adjusted so that the rod temperature during reelingwas reduced to between 1000 and 1225 F. and so that the surfacetemperature did not fall below 1000 F. The rod had a fine pearliticstructure with small grain size and drew satisfactory tour drafts to0.095" diameter for a total reduction of area of 75%. The grain size ofthe rod subjected to the two step controlled cooling in accordance withthe invention was actually smaller than is frequently obtained in aconventional patenting operation, although the total permissiblereduction in area was somewhat less than can be achieved with such apatenting operation.

In another example of the invention some 0.218" diameter steel rodcontaining 0.65% carbon was subjected to the first cooling step of theinvention and was delivered to a pouring reel with a rod surfacetemperature of 1400 F. The rod was sprayed with atomized water to effectthe second cooling step of the invention while the rod was being reeled.The cooled rod had a fine pearlitic structure and drew satisfactorilyfour drafts to 0.115" diameter for a total reduction of area of 72%. V

In contrast to these examples, a 0.218" diameter rod containing 0.65%carbon as hot rolled without special cooling (only the usual waterquenching) had a coarse pearlitic structure and broke on drawing threedrafts to 0.135" diameter, for a total reduction in area of 62%.

An important advantage obtained by the rapid controlled cooling of rodin accordance with the invention is a reduction in the formation ofscale. With large compact rod coils finished at a high temperature,scale is commonly as much as 1.5% of'the weight of the coil. By rapidlycooling the rod in accordance with the method of the invention, scalecan be reduced to within the range of 0.25 to 0.5% of the weight of thecoil. Lower scale not'only represents a saving in steel but also asaving in acid used subsequently to remove the'scale.

While the invention has been described in connection with specific stepsand in specific uses, various modifications thereof will occur to thoseskilled in the art without departing from the spirit and scope of theinvention as set .forth in the appended claims.

What is claimed is:

l. A method of heat treating hot rolled high carbon steel rod,comprising subjecting the rod to a water quenching as the rod travelsfrom the rolls to a coiling device, said water quenching cooling the rodto an average temperature above the critical temperature at whichcarbide comes out of solution and a surface temperature not below about900 F, said rod having a surface temperature lying Within the range ofabout 1350 to 1450 F. when entering the coiling device, and sprayingsaid rod with atomized water while being coiled on said device to reducethe temperature throughout the cross section of the rod to within therange of about l000-l225 E, the surface temperature of said rod duringat least the major portion of said coiling not being below about 1000 F.

2. A method of heat treating hot rolled high carbon steel rod,comprising subjecting the rod to a Water quenching intermediate therolls and a coiling device rapidly to cool the rod but without producingsubstantially different microstructures at the outside and center of therod and whereby the surface temperature of the rod on tering saidcoiling device lies in the range of about 1350- 1450" F., and sprayingatomized water on the rod While said rod is being coiled on said deviceto reduce the temperature throughout the cross section of the rod tovalues lying within the range of about 900-1300" F.

3. A method of heat treating hot rolled high carbon steel rod,comprising subjecting the rod to a water quenching intermediate therolls and a coiling device rapidly to cool the rod but Without producingsubstantially different mircostructures at the outside and center of therod, allowing at least partial equalization of the center and outsidetemperatures of the quenched rod whereby the surface temperature of therod entering the coiling device lies within the range of about 1350-1450F., and spraying atomized water on the rod while the rod is being coiledon said device to reduce the temperature throughout the cross section ofthe rod to values lying within the range of about 900-1300 F.

4. A method of heat treating hot rolled high carbon steel rod whichleaves the rolls at a speed'of the order of 3000-5000 feet per minuteand a temperature of the order of 165 -1800" F comprising subjecting therod to a water quenching as the rod travels from the rolls to a coilingdevice, said water quenching cooling the rod to an average temperatureabove the critical temperature at which carbide comes out ofsolution'and a surface temperature not below about. 900 F., allowing atleast partial equalization of the center and outside temperatures of thequenched rod ,wherebythe surface temperature of i the rod entering thecoiling device lies within the range 1 I of about 135 0-145 0 F., andfurther cooling the rod while the rod is being coiled by sprayingatomized water thereon, said further cooling reducing the temperaturethroughout the cross section of the rod to values lying within the rangeof about 900-1300" F;

5. A method of heat. treating hot rolled high carbon steel rod Whichleaves the rolls at ai speed of the order of 3000-5000 feet per minuteand a temperature of the order of p 1650-1800 -F., comprising subjectingthe rod to a 'water quenching as the rod travels from theirolls to a.coiling device, said water-quenching coolingthe rod to an averagetemperature lying above about 1340" F. and a surface temperature notbelow about 900 F., allowing at least partial equalization of the centerand outside temperatures of the quenched rod whereby the surfacetemperature of the rod entering the coiling device lies within the rangeof about l350-l450 F., and further cooling the rod while the rod isbeing coiled by spraying atomized water thereon, said further coolingreducing the temperature throughout the cross section of the rod tovalues lying within the range of about 900-1300" E, the surfacetemperature of the rod throughout the coiling operation not fallingbelow about 900 F.

6. A method of heat treating hot rolled high' carbon steel rod whichleaves the rolls at a speed of the order of 3000-5000 feet per minuteand a temperature of the order of 1650-1800 F., comprising subjectingthe rod to a water quenching as the rod travels from the rolls to acoiling device, said Water quenching cooling the rod to an averagetemperature above the critical temperature at which carbide comes out ofsolution and a surface temperature not below about 900 F., allowing atleast partial equalization of the center and outside temperatures of thequenched rod whereby the surface temperature of the rod entering thecoiling device lies within the range of about 1350-1450 PI, and furthercooling the rod while the rod is being coiled by spraying atomized waterthereon, said atomized water being sprayed primarily on the uppermostlayer of coiled rod, the volume of water flow and the degree ofatomization thereof being adjusted so that said further cooling reducesthe temperature throughout the cross section of the rod to values lyingwithin the range of about 900-1300 F.

7. A method as set forth in claim 6 in which said coiling devicecomprises a pouring reel and said spray is directed. primarily at alimited area of the uppermost layer of rod being coiled.

8. A method as set forth in claim 6 in which said coiling devicecomprises a laying reel and said spray is formed by a plurality ofindividual spaced sprays, adjacent sprays having overlapping areas ofcontact with the uppermost layer of said coil whereby all portions ofthe coil are subjected to said further cooling step.

9. A method of heat treating hot rolled high carbon steel rod,comprising subjecting the rod to a water quenchintermediate the rollsand a coiling device rapidly to cool the rod but without producingsubstantially diiierent microstructures at the outside and center of therod and whereby the surface temperature of the rod entering the rod isbeing coiled on said device, said atomized water being directedprimarily on at least a portion of the uppermost layer of the coil beingpoured on said device and the flow and extent of atomization of saidwater being adjusted so as to reduce rapidly the temperatures of allportions of the cross section of the rod to values below the criticalvalue at which carbide comes out of 'solution, the temperature at thesurface of the rod being maintained at a value not below about l000 F.during formation of the coil. i 7

10. in a method of preparing. carbon steelrods for wire drawing by heattreating a rod as'it leaves a hot rolling mill at a temperature of theorder of 1650- 1800 F., the rod being fed to a coiling device with acrostructures at the outside and center of the rod and whereby thesurface temperature of the rod entering said coiling device lies in therange of about l3501450 F., and spraying atomized water on the rod Whilesaid rod is being coiled on said device to reduce the temperaturethroughout the cross section of the rod to values lying within the rangeof about 90()l300 F.

12. A method of eat treating hot rolled low carbon steel rod, comprisingsubjecting the rod to a Water quenching intermediate the rolls and acoiling device rapidly to cool the rod but without producingsubstantially different microstructures at the outside and center of therod, allowing at least partial equalization of the center and outsidetemperatures of the quenched rod whereby 10 the surface temperature ofthe rod entering the coiling device lies Within the range of about1350-1450 F., and spraying atomized water on the rod While the rod isbeing coiled on said device to reduce the temperature throughout thecross section of the rod to values lying within the range of about900-1300 F.

References Cited in the file of this patent UNITED STATES PATENTS2,658,012 Strachan Nov. 3, 1953 2,75 6,169 Corson et al July 24, 19562,810,570 Wilson Oct. 22, 1957

2. A METHOD OF HEAT TREATING HOT ROLLED HIGH CARBON STEEL ROD,COMPRISING SUBJECTING THE ROD TO A WATER QUENCHING INTERMEDIATE THEROLLS AND A COILING DEVICE RAPIDLY TO COOL THE ROD BUT WITHOUT PRODUCINGSUBSTANTIALLY DIFFERENT MICROSTRUCTURES AT THE OUTSIDE AND CENTER OF THEROD AND WHEREBY THE SURFACE TEMPERATURE OF THE ROD ENTERING SAID COILINGDEVICE LIES IN THE RANGE OF ABOUT 13501450*F., AND SPRAYING ATOMIZEDWATER ON THE ROD WHILE SAID ROD IS BEING COILED ON SAID DEVICE TO REDUCETHE TEMPERATURE THROUGHOUT THE CROSS SECTION OF THE ROD TO VALUES LYINGWITHIN THE RANGE OF ABOUT 900-1300*F.